For fulfilling their functions in a reliable and durable manner, implantable medical devices like, for example, heart pacemakers or implantable cardioverters require robust contact of their respective actuator and/or sensor portions (in particular, stimulating and/or sensing electrodes) with the bodily tissue onto which they act or from which they derive sensor signals. Therefore, for decades considerable efforts have been put into developing fixation mechanisms which are both easy to operate and reliable. Nevertheless, as during the implantation of an implantable medical device there can be no absolute certainty as to the initial quality and/or durability and/or robustness, respectively, of the contact between device and tissue, it is vital to test the contact quality/durability/robustness.
For example, in commercially-deployed pacemaker lead designs, few, if any, mechanisms have been developed to offer built-in feedback/confirmation capabilities for assessing robust mechanical engagement between the lead fixation devices and the patient's myocardium. While other tangentially-leveraged strategies (see further below) have historically helped to overcome such shortcomings, recent efforts centered on the development of injectable leadless pacemaker designs present heightened needs for the prevalence of such anchoring validation schemes.
In leadless pacemakers, the delivery of pacing waveforms is weaned from the use of explicit, wired linkages to distally-stationed pulse generation units. Most proposed configurations have explored myocardial interfacing through intravenous, injectable implantation. In such systems, the devices reside within targeted heart chambers. Compared to traditional lead-reliant pacing strategies, if fixturing fails at any point, the devices are not tethered to remote units capable of providing backup anchoring. Device dislodgement in such contexts would knowingly lead to pulmonary and/or stroke complications, thus creating a greater risk to patient well-being than typical pacing approaches.
Presently, no direct method exists for assessing the effectiveness of mechanical interfacing between the lead and/or device anchors and the patient's myocardium. The dominant technique for lead-based fixation benchmarking leverages instead indirect fluoroscopy visualization techniques coupled with a withdrawal of the manipulation stylet to monitor for changes in lead tip displacement. If the withdrawal of the stylet motivates no noticeable change in the location of the lead tip, then it is assumed to have engaged with the myocardium. The efficacy of that engagement is then further validated, by checking electrical impedance readings, along with sensing and pacing thresholds. In the case of injectable leadless pacemakers, a move functionally equivalent to the withdrawal of the manipulation stylet would center on the delivery catheter releasing the device after performing an anchoring procedure.
The drawbacks associated with the stated approaches for monitoring fixation quality motivate a variety of technical support tasks. Lacking explicit mechanical interface state reporting, in general, creates a need for significant amounts of guesswork during implant in the context of both active lead placement and the installation of injectable leadless pacemaker designs. Uncertainty regarding the condition of the anchoring within the myocardium thereby unwittingly inflates the scheduled amount of time necessary for affiliated implant procedures. Part of this inflation is grounded in the diligence required to leverage impedance and sensing/capture thresholds as indirect fixture validation metrics. To properly measure such attributes of a pacing system, explicit, monitored testing procedures must occur to provide proper scrutiny of the retention response. In cases where poor fixation occurs, the lead and/or device must be repositioned and then the full sequence of electrical validation processes must be repeated until appropriate levels are reported. To complicate matters further, all of the efforts mentioned above are surrogate attempts to qualify fixation quality, and a keen risk still exists that the implanter would not realize that the device had been installed improperly. Such a condition could demand subsequent follow-up procedures that could prove even more invasive than the initial implant.
The present invention is directed toward overcoming one or more of the above-identified problems.